Not Applicable.
The present invention relates generally to solvent extraction processes for recovery of metal values from aqueous solutions and, more particularly, to a method of separating copper from iron resulting in a large improvement in the recovery of copper over iron.
Copper is generally obtained from its ore by a solvent extraction process wherein copper is in an aqueous leach solution obtained from a body of ore which contains a mixture of metals in addition to copper. The leaching medium dissolves salts of copper and other metals as it trickles through the ore, to provide an aqueous solution of the mixture of metal values. The metal values are usually leached with sulfuric acid medium, providing an acidic aqueous solution. The aqueous solution is mixed in tanks with an extraction reagent which is dissolved in an organic solvent, e.g., a kerosene. The reagent includes an extractant chemical which forms a metal-extractant complex with the copper ions in preference to ions of other metals. The step of forming the complex is called the extraction or loading stage of the solvent extraction process. The outlet of the mixing tanks is continuously fed to a large settling tank, where the organic solvent or organic phase, now containing the copper-extractant complex in solution, is separated from the depleted aqueous solution or aqueous phase. This part of the process is called phase separation. Usually, the process of extraction is repeated through two or more mixer-settler stages, in order to more completely extract the copper.
Among the more problematic copper bearing feedstocks treated in conventional solvent extraction processes are those in which quantities of dissolved iron values range from about 1 gpl or 20 gpl. Frequently the extractant chemical employed will form an iron-extractant complex which, in turn, results in the presence of iron in the strip aqueous phase. Where electrowinning is employed to recover copper from the strip aqueous solution, the presence of iron will complicate recovery by decreasing current efficiency. To avoid such problems, a more or less constant xe2x80x9cbleedxe2x80x9d of the tankhouse solution is established, with the solution bled off being circulated back into the initial feedstock or to the leach pile itself. Because such tankhouse bleed solutions contain appreciable amounts of copper and acid, efficiency of the entire system can be compromised.
The currently more favored reagents employed in recovery of copper values from aqueous solutions having iron values present are those which exhibit a relatively high degree of copper/iron selectivity, i.e., those which, under standard operating conditions, extract a high proportion of the copper present in the feedstock but only a minor proportion of the iron present. Among the reagents credited with displaying good copper/iron selectivity characteristics are those including hydroxy aryl oxime extractants such as long chain alkyl or alkenyl solubilized hydroxy aryl aldoximes and ketone oximes. See, for example, Birch, xe2x80x9cThe Evaluation of the New Copper Extractant xe2x80x98P-1xe2x80x99xe2x80x9d appearing in the Proceedings of the 1974 International Solvent Extraction Conference, pp. 2837-2871, wherein xe2x80x9chigh selectivity against Fe (III) . . . in the sulphate systemxe2x80x9d is attributed to a reagent containing a 2-hydroxy-5-nonyl benzaldoxime extractant. Ketoximes such as 2-hydroxy-5-alkylphenyl ketoximes have also been used to selectively remove copper as described in U.S. Pat. No. 5,670,035, the entire contents of which are incorporated herein by reference. Each of the above-noted hydroxy aryl oxime-containing reagents has proven to extract undesirable amounts of iron from copper and iron-bearing ores. As a result, recovery of copper from such solutions necessitates at least some bleeding off of tankhouse solutions with losses to the overall economy of the system. Thus, there is a need to selectively remove copper to the more complete exclusion of iron from aqueous solutions containing copper and iron.
One aspect of the present invention pertains to a process for the separation of copper from iron in an aqueous feedstock solution containing dissolved copper and iron values comprising contacting the feedstock solution with a water-immiscible organic solution comprised of a hydrocarbon solvent and a compound of the formula I 
wherein R5 is a C1-22 linear or branched alkyl group, a C2-22 linear or branched alkenyl group, a C6 aryl group, a C7-22 aralkyl group, a halogen, OH or xe2x80x94OR6 wherein R6 is a C1-22 linear or branched alkyl group, a C2-22 linear or branched alkenyl group, a C6 aryl group, a C7-22 aralkyl group; R1 is hydrogen, or a C1-22 linear or branched alkyl or alkenyl group, a C6 aryl group or a C7-22 aralkyl group; R2-R4 is hydrogen, halogen, a linear or branched C6-12 alkyl group, xe2x80x94OR6 wherein R6 is a C1-22 linear or branched alkyl group, a C2-22 linear or branched alkenyl group, a C6 aryl group, or a C7-22 aralkyl group to form an aqueous phase comprised of iron and an organic phase comprised of the hydrocarbon solvent and a copper-extractant complex wherein the copper-extractant complex is soluble in the hydrocarbon solvent. The R2-R5 groups are chosen so that the copper-extractant complex is soluble in the hydrocarbon solvent. After the extraction stage is completed and the organic and aqueous phases separate, the organic phase is substantially free of iron and/or an iron-extractant complex.
Another aspect of the invention pertains to novel ketoximes which are useful as extractants for copper and which are compounds of the formula II 
wherein R11 is a C1-22 linear or branched alkyl group, a C2-22 linear or branched alkenyl group, a C6 aryl group, a C7-22 aralkyl group, a halogen, OH or xe2x80x94OR6 wherein R6 is a C1-22 linear or branched alkyl group, a C2-22 linear or branched alkenyl group, a C6 aryl group, a C7-22 aralkyl group; R7 is a C1-22 linear or branched alkyl or alkenyl group, a C6 aryl group or a C7-22 aralkyl group; branched alkyl group, a C2-22 linear or branched alkenyl group, a C6 aryl group, a C7-22 aralkyl group, a halogen, OH or xe2x80x94OR12 wherein R12 is a C1-22 linear or branched alkyl group, a C2-22 linear or branched alkenyl group, a C6 aryl group, a C7-22 aralkyl group; R7 is a C1-22 linear or branched alkyl group, a C2-22 linear or branched alkenyl group, a C6 aryl group or a C7-22 aralkyl group; R8-R10 is hydrogen, halogen, a linear or branched C6-12 alkyl group, xe2x80x94OR12 wherein R12 is a C1-22 linear or branched alkyl group, a C2-22 linear or branched alkenyl group, a C6 aryl group, or a C7-22 aralkyl group with the proviso that the total number of carbon atoms in R8-R10 is at least 7.
Not Applicable.
In the process for the separation of copper from iron in an aqueous feedstock solution containing dissolved copper and iron values, the feedstock solution is contacted with a water-immiscible organic solution comprised of a hydrocarbon solvent and a compound of the formula I 
wherein R5 is a C1-22 linear or branched alkyl group, a C2-22 linear or branched alkenyl group, a C6 aryl group, a C7-22 aralkyl group, a halogen, OH or xe2x80x94OR6 wherein R6 is a C1-22 linear or branched alkyl group, a C2-22 linear or branched alkenyl group, a C6 aryl group, a C7-22 aralkyl group; R1 is hydrogen, or a C1-22 linear or branched alkyl or alkenyl group, a C6aryl group or a C7-22 aralkyl group; R2-R4 is hydrogen, halogen, a linear or branched C6-12 alkyl group, xe2x80x94OR6 wherein R6 is a C1-22 linear or branched alkyl group, a C2-22 linear or branched alkenyl group, a C6 aryl group, or a C7-22 aralkyl group to form an aqueous phase comprised of iron and an organic phase comprised of the hydrocarbon solvent and a copper-extractant complex wherein the copper-extractant complex is soluble in the hydrocarbon solvent. The R2-R5 groups are chosen so that the copper-extractant complex is soluble in the hydrocarbon to the extent of at least about 1 g/l Cu solubility, preferably at least 5 g/l.
The compounds of the formula I that can be used in the process according to the invention can be made by a number of different methods known to those skilled in the art. For example, 3-methyl-5-nonylsalicylaldoxime can be made by reacting o-cresol with tripropylene in the presence of an acid catalyst such as AMBERLYST(copyright) 15 resin to form 4-nonyl-2-cresol which is in turn converted to the aldehyde by reaction with para-formaldehyde in the presence of a catalyst such as titanium cresylate. The 3-methyl-5-nonylsalicylaldehyde is then reacted with hydroxylamine sulfate to form the 3-methyl-5-nonylsalicylaldoxime. In all cases, the total number of carbon atoms in all of R2-R5 groups must be great enough so that the corresponding copper-extractant complex is soluble in the hydrocarbon solvent.
The hydrocarbon solvent can be any liquid organic compound having a dielectric constant of up to about 2.5. Examples of such liquids include, but are not limited to, liquid alkanes such as pentane, hexane, heptane, octane, nonane; liquid aromatic compounds such as benzene, toluene, o-, m- and, p-xylene. Preferred solvents are those having flash points of about 150xc2x0 F. or higher and solubilities in water of less than about 0.1.
The feedstock solution containing dissolved copper and iron values is contacted with the water-immiscible organic solution comprised of a hydrocarbon solvent as described herein and a compound of the formula I for a period of time sufficient to allow the oxime described herein to a form complex with the iron and copper ions. The feedstock can be contacted by the organic solution in any manner that brings the two immiscible phases together for a period of time sufficient to allow the compounds of formula I to a form complex with the iron and copper ions. This includes shaking the two phases together in a separatory funnel or mixing the two phases together in a mix tank as described in U.S. Pat. No. 4,957,714, the entire contents of which is incorporated herein by reference.
While not wishing to be bound by theory, it is believed that the increased copper/iron selectivity of the process according to the invention is due to the decreased stability of the iron complex of the 3-substituted oximes relative to the corresponding copper complex. This stability difference is related to the structure of the oximes of formula I. The copper complexes of the 3-substituted oximes are more stable than the iron-complexes of the 3-substituted oximes. This stability difference is not as great in copper and iron complexes of oximes of the formula I that are unsubstituted at the 3-position (wherein R5 is hydrogen). Since the iron complex is less stable for the 3-substituted oximes, it is present in a relatively low concentration.
The process according to the invention is also applicable to systems wherein the aqueous feedstock is a concentrate leach solution and/or a bioleach solution. These solutions tend to have higher acid concentrations as described in U.S. Pat. Nos. 5,698,170 and 5,895,633, the entire contents of each of which is incorporated herein by reference, and in many cases higher iron concentrations than most current oxide heap leach solutions. The 3-methyl ketoximes as described herein are especially preferred for such applications.
The following examples are meant to illustrate but not to limit the invention.